A tweeter is used to produce high audio frequencies, typically from around 2 KHz to around 20 KHz. High frequency sound waves are created by the vibration of the air by a diaphragm of the tweeter. The diaphragm of the tweeter generally is light and stiff in order to have frequency response extending to the upper range of human hearing around 20 kHz. Best performing diaphragms are made of thin metal sheet, such as Aluminum, Titanium, Beryllium or sometimes ceramic. Due to the mass constraints, the thickness of a diaphragm is typically a few hundredth of a millimeter. This makes the diaphragm very fragile. Therefore, there is a need to put a protective screen in front of the diaphragm to prevent accidental damage from foreign objects coming into contact with the diaphragm of the tweeter.
On the other hand, as frequencies of sound waves radiated by the diaphragm increase, the lengths of the sound waves decrease and at some points become comparable to the size of the diaphragm. Sometimes, due to different distances between the position of the listener and different portions of the diaphragm, the sound waves radiated from different portions of the diaphragm reach the position of a listener at slightly different times. As a result, the phases of the sound waves reached the position of the listener may be misaligned. Due to the phases misalignment, the amplitudes of these sound waves sometimes add up when they are in phase or subtract when out of phase. This creates unevenness in frequency response of the sound waves received by the listener.
Phase plugs are commonly used to improve the unevenness in frequency response caused by phases misalignment of the sound waves. For example, sound waves from certain portions of the diaphragm of the loudspeaker can be suppressed by a phase plug to reduce the effect of phase misalignments of sound waves received by the listener, and thus to improve the unevenness in frequency response.
Sometimes, an assembly combining a tweeter screen and a phase plug is used to both protect the diaphragm and mitigate sound wave, phase misalignment. However, the assemble requires the screen and the phase plug to be manufactured separately. In use, the screen and the phase plug need to be assembled, for example, by adhesives. In addition, the assemble may not be reliable as the screen and the phase plug may be detached from each other due to the failure of the adhesives.